There are many systems which make use of elongated metallic guides for guiding the movement of a body along the guide. The guide itself is supported at spaced intervals which present problems for testing for weaknesses in the guide.
One example of the type of arrangement described above is the standard aerial tram system in which a cable car is supported by rides along a wire rope located above the cable car. This wire rope is supported along its length by spaced apart towers with long stretches of rope between the towers. It is imperative that these long stretches of rope be tested for weaknesses which could affect safety of the system.
There are presently available a number of different types of wire rope testing devices, one of which is a DC wire rope tester which is a device that is arranged to induce a magnetic field in the section of rope located within the device and to test for flux leakages radially of the main magnetic field. These flux leakages are indicative of weaknesses such as fraying or corrosion of the wire rope.
According to standard construction, conventional DC wire rope testers comprise two substantially identical housing sections having strong permanent magnets in each of the housing sections and a search coil located within the tester. In order to use the tester for purposes of checking the strength of the steel wire rope in a cable car system the tester is secured behind one of the cable cars which rides along the steel wire rope pulling the tester with it. The tester itself is wrapped completely around the rope behind the cable car.
This prior art arrangement in extremely awkward to work with due to the presence of the support towers acting as a block to the travel of the tester when it is closed around the rope. Therefore, it is necessary for an individual in the cable car to stop the car in advance of the tower and to climb out onto the cable for opening the tester to allow it to clear past the tower and to then reclose the tester after it has passed by the tower. A manual opening and closing of the tester while the operator is standing out on the cable is time consuming and can be extremly dangerous even under the best of conditions and in curcumstances where the cable is at an awkward angle or where there is inclement weather the difficulties of opening and closing the tester are further increased. Added to this are the difficulties presented by the weight of the housing section that must be opened and closed and the magnetic attraction which has to be overcome to open the tester due to the provision of strong permanent magnets in each of the housing sections.
In an attempt to overcome this problem of clearing the tester past the towers arrangements have been used which comprise only the upper housing section of the tester with the lower housing section being completely removed from the tester. The problem with this particular arrangement is that it does not completely surround the rope and therefore does not provide thorough testing results. For example, the sensors in the upper housing sections may not detect breakages or discontinuities along the lower untested half of the rope.
There are setups other than the cable car system described above which also incorporate elongated magnetically permable guides which have to be tested for strength. These setups again present problems at the support positions to the clearance of the tester along the object.